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Date:   Tue, 20 Aug 2019 18:48:58 -0700
From:   Christoph Hellwig <hch@infradead.org>
To:     Vlastimil Babka <vbabka@suse.cz>
Cc:     Christoph Hellwig <hch@infradead.org>, dsterba@suse.cz,
        Christophe Leroy <christophe.leroy@c-s.fr>,
        erhard_f@mailbox.org, Chris Mason <clm@fb.com>,
        Josef Bacik <josef@toxicpanda.com>,
        David Sterba <dsterba@suse.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        linux-btrfs@vger.kernel.org, linux-mm@kvack.org,
        stable@vger.kernel.org, Dave Chinner <david@fromorbit.com>
Subject: Re: [PATCH] btrfs: fix allocation of bitmap pages.
Message-ID: <20190821014858.GA9158@infradead.org>
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On Tue, Aug 20, 2019 at 01:06:25PM +0200, Vlastimil Babka wrote:
> > The whole point of copy_page is to copy exactly one page and it makes
> > sense to assume that is aligned.  A sane memcpy would use the same
> > underlying primitives as well after checking they fit.  So I think the
> > prime issue here is btrfs' use of copy_page instead of memcpy.  The
> > secondary issue is slub fucking up alignments for no good reason.  We
> > just got bitten by that crap again in XFS as well :(
> 
> Meh, I should finally get back to https://lwn.net/Articles/787740/ right

Yes.  For now Dave came up with an idea for a workaround that will
be forward-compatible with that:

https://www.spinics.net/lists/linux-xfs/msg30521.html